Electric circuits



W. J. 'M LACHLAN El AL ELECTRIC CIRCUITS Filed Jan. 25', 1939 CURRENT TRANSFORMER 4 Sheets-Sheet l 7' Fug l.

F'Ok THREE pmss-Jofiumya CURRENT) RES/ST'AAIC PEA OT'ANCE 5 CUMPENJA T/ON COMPEN$A r 1 0M I POTENTIAL a (R=/.00) D (R =1. 75) RE m4 usromnm Y J, 9 II (X =I.75) E Fig. 2.

ass/sumo: nawnwcz COMPENSATION coups/m4 T'lmv g (R-l.00) (r? 1.7.?)

Inventors 1 Willard J. McLachlan, Wayne R. Sir-chard,

JMZM

Their- Attorney.

Jan 2, 1940. w. J. MCLACHLAN ET AL 2,185,707

ELECTRIC CIRCUITS Filed Jan. 25, 1959 4 Sheets-Sheet 2 Pig. 6.

lnven torsz" Willard J. McLachlan, Wayne E. Birchard,

8 Th ir Attorneg.

Jan. 2, 1940. w. J. MOLACHLAN El AL- 2,185,707

ELECTRIC CIRCUITS Filed Jan. 25, 1939 4 Sheets-Sheet 4 Inventors 7 h Willardd. McLachlan,

Wayne BBir haw-d by Them Ator ney.

Patented-Jan. 2, 1940 UNITED STATES ELECTRIC, CIRCUITS I Willard J. Momma, Scotia, N. Y., and Wayne E. Bil-chard, Pittsiield, Masa, assignors to General Electric Company, a annotation of New. York I Application January 25, 1939, Serial No. 252,814

' 23 Claims. ((11.171-119) This invention. relates to electric circuits and more particularly to improvements in adjustable voltage phase shifting circuits for general use and particularly for use in line drop compensators for single phase automatic, feeder voltage regulators adapted to be connected open-delta in three phase power lines.

This application is a continuation in part of our application Serial No. 188,492, filed February 3, 1938 and assigned to the assignee of this application. a

As its name implies, a line drop compensator is a device which produces compensation for the voltage drop in an electric line. When used with an automatic voltage regulator, it permits the primary voltage sensitive device to measure, in effect, the voltage at a point farther out on the line than its actual point of connection, such as at a so-called center of distribution. By its use, regulators may be located in substations 'or at other points on a power system more or less remotely located from the loads connected to the system. v

A common way of regulating the voltage of a 3-phase feeder circuit is by means of two single phase regulators connected respectively in two of the line conductors of the circuit. Such a connection is commonly referred to as an opendelta connection because only two of the three voltages of the circuit are regulated directly, the third voltage being regulated indirectly by means of the triangular relationship of the three voltages. winding, which is connected in one of the lines of the circuit, and a shunt winding which is 'connected between the line in which its series winding is connected and one of the remaining lines. In other words, in connecting a single phase regulator to'a 3-phase,line, as far as the regulator proper is concerned, connections are made to only two of the three lines of the circuit. It is, therefore, desirable that the regulator auxiliaries and control circuits beenergized from these same connections to the power circuit, as otherwise, the expense of installations may be considerably increased by having to make a con-' -nection to the third one of'the' circuit conductors. However, in a 3-phase circuit at unity power factor, the line to line voltage and theline current are displaced 30 in phase, this angle being an Each single phase regulator has a series angle of lead or an angle of lag depending on the direction of phase rotation. Also, the resistance drop in the line at unity power factor is in phase opposition to the phase voltage and the reactance drop in the lineis in quadrature lagging with respect to the phase voltage. Consequently, an ordinary line drop compensator adapted for simple single phase operation will not give true line drop compensation when the compensator current is displaced from the voltage of the voltage sensitive circuit. 1

In accordance with this invention there is provided a relatively simple and inexpensive compensator which corrects for the 30-de'gree shift and which does not require auxiliary current transformers or interconnections between regulators. I

The invention is characterized by elements consisting of net works of parallel connected reactances and adjustable resistors or reactors wherein the adjustment of the resistors or reactors determines the magnitude of the com- A further object of the invention is to provide a new and improved line drop compensator.

Another object of the invention is to provide an inexpensive line drop compensatoradapted for use with open-delta connected, single phase feeder voltage regulators.

The invention will be better understood from the following description taken in connection with the accompanying'drawings and its scope will be pointed out in the appended claims.

In the drawings, Fig. 1 is a diagrammatic illus tration of an embodiment of the invention adapted for use with compensator currents which lead the line voltage by 30 with unity power facts:

load, Fig. 2 is similar to Fig. l but is adapted for use with compensator currents which lag the line voltage by 30 with unity power factor load, Fig. 3 is a diagram of an element of the com-- pensators of Figs. 1 and 2, Figs. 4, 5; 6 and l are vector diagrams for illustrating the operation the. invention, Fig. 8 illustrates diagrammatical- 1y what may be referred to as a universal com pensator which comprises the compensators of Figs. 1 and 2, and also may be used with single phase circuits, Fig. 9 is a modified universal compensator, Fig. 10 is a generalized diagram of a. compensator element of Fig. 9, Fig. 11 is a modified form of the universal compensator shown in Fig. 9, Figs. 12 and 13 illustrate modifled ways of adjusting the voltage or compensator setting and Figs. 14 and 15 illustrate modifications employing the adjusting means of Fig. 13.

Referring now to the drawings and more particularly to Fig. 1, there is shown therein a.,3- phase power circuit I in the lowermost conductor of which there is connected a current transformer 2 and between whose center and lowermostv conductors there is connected potential transformer 3. Potential transformer 3 energizes a relatively high impedance voltage sensitive circuit 4 containing any suitable voltage sensitive device 5 such, for example, as a primary relay, contact-making voltmeter or resonant circuit. Connected in the voltage responsive circuit is a line drop compensator 6 having a resistance compensation element consisting of a potentiometer or slide wire type adjustable resistor 8 connected in parallel with a capacitor 9 and having a reactance compensation element consisting of a slide .wire type resistor in connected in parallel with a reactor II. The ratio in ohms of resistor 8 to capacitor 9 is 1.00 1.73, while the ratio in ohms of resistor l0 to reactor II is 1.73 1.00.

Fig. 2 difiers from Fig. 1 in that the capacitor 9 of the resistance compensation element of Fig. l is replaced by a reactor i2, while the reactor ll of the reactance compensation element of Fig. l is replaced by a capacitor l3. In order vectorially to reverse the voltage drop of capacitor. |3, for reasons which will be explained hereinafter, a transformer I4 is interposed between the capacitor l3 and the rest of the circuit. The ratio of resistance to reactance in both the resistance and reactance compensation elements of Fig. 2 is numerically the same as in Fig. 1.

The operation of Figs. 1 and 2 can best be understood by first referring to Fig. 3 which illustrates an element of one of the compensators. Specifically, it resembles most closely the reactance compensation element of Fig. 1 in that it consists of a slide wire resistor R paralleled by a reactor X. A current I enters this circuit through a. conductor 2' and leaves it through a conductor 2". In position a of the slide wire, wherein the resistance R and reactance X are directly in parallel, the current I divides part of it. IR going through the resistance R and the remaining part of it, Iz going through the reactance X. If the slide wire adjuster associated with the conductor 2' is now moved to the left successively to positions b, c, and d, IR. will progressively increase as it flows successively through less resistance, designated as Rh, Re, and Rd, while at the same time Iz will progressively decrease as it will have to flow successively through impedances consisting in position b of r 0] in position 0 of etc., it being understood, of course, that the indicated additions are vector additions. This change in the relative impedance values of the two branches of the circuit as the slide wire is moved is clearly shown in Fig. 4, this figure automatically making the vector addition of X plus the other varying values of resistance so as to give successively the impedance values Zn, which equals X in position a of the slide wire, and Z, Zc, and Zd corresponding respectively to the positions b, c, and d of the slide wire. It will also be observed that in Fig. 4, if X has a value of unity, R has a value of approximately 1.73. This is the ratio of R and X given for the reactance compensation element of Fig. 1. The currents and voltages in Fig. 3 are shown vectorially in Fig. 5. This figure is essentially the same as Fig. 4 by reason of the fact that the current divides in such a manner that current in one parallel branch is proportional to the impedance of the other branch. Thus is proportional to R Iz to R etc.

I while I1 In etc. I

- are proportional respectively to Z3, Zb, etc. The

voltage E produced by the compensator element is, of course, the voltage drop through the reactor X. In Fig. 5 this voltage will be proportional in magnitude to Iz and will be lagging it 90 degrees in phase. It may, therefore, conveniently be represented by the vectors Ea, Eb, E0 and Ea corresponding respectively to the similarly lettered positions of the slide wire in Fig. 3.

From the above, it follows that Fig. 3 has the interesting property that the phase of the voltage E is independent of the position of the slide wire, while its magnitude is directly proportional to the position of the slide wire.

It will also be noted that the vector voltages-E in Fig. 5 lag by about 30 degrees the voltage drop which would be produced in a reactor if it carried the current I. Therefore. Fig. 5 represents the vector relations in the reactance compensation element of Fig. 1 because if the total current I in Figs. 3 and 5 advanced 30 degrees, that is to say, if the entire vector diagram of Fig. 5 is rotated counter-clockwise 30 degrees, the voltages E will have the conventional vertically downward direction representing a quadrature lagging reactance drop.

This is better explained by reference to Fig. 6 in which'the horizontal vectors to the right of the zero point are, respectively, the current and voltage of a unity power factor single phase circuit, while the horizontal and vertical downward vectors to the left of the zero point are the resistance and reactance drops respectively in the circuit. If now the current is shifted 30 degrees in either the lagging or the leading.direction, the resistance and reactance drops are similarly shifted. The vector diagram of the voltage responsive circuit 4 of Figs. 1 and 2 is exactly the same as that of Fig. 6 except on a smaller scale, and the 30 degree shifted resistance and reactance drops indicated by the dashed lines represent the resistance and reactance compensation which would be secured'by a conventional single phase line drop pompensator if con nected to a 3-phase circuit as in Fig.1. The

proper resistance and reactance compensation voltages are those shown by the continuous resistance and reactance drop vectors in Fig. 6 from which it will be seen that when the current lags the voltage by 30 degrees, the compensator voltages should be shifted 30 degrees ahead in. a leading direction in order-to get true compensation, whereas if the current leads the volta e by 30 degrees, the compensator voltages should be shifted back 30 degrees in a lagging direction in order to secure correct compensation.

In Fig. 7, there are combined i'our diagrams similar to Fig. 5. Each of these diagrams represents conditions in a different one of the elements. of 'Figs. 1 and 2. The heavy lines, both solid and dashed, denote resistance compensation, the light lines, both solid and dashed, 'denote reactance'compensation, the solid lines denote compensation for use with 30 degreelagging current (Fig. 2) and the dashed lines denote compensation for use with 30 degree leading current (Fig. 1). For example, consider the rectangle-composed of the heavy and light dashed lines. The vector x1.=1.o o corresponds to reactor ll, while the vector R=1.73 denotes resistor ll. The-reactance compensation voltage is at right angles to the resistance vector III, as in Fig. 5, and lags the .correct reactance compensation voltage (as shown by D! in Fig. 6) by 30 degrees so that if the compensator current .represented by .the horizontal diameter in Fig. 'l is rotated 30 degrees in the leading direction, the entire vector diagram will rotate through. a similar angle and the reactance compensation volt age will coincide in phase with the correct reactance compensation. Similarly, the heavy dashed vector R=l.00.denotes resistor 8 and the heavy dashed vector'xa=l.73 denotes the capacitor 9 in Fig. 1. The compensation voltage produced by the resistance compensation element of Fig. 1' will be at right angles to the vector 8 and, like the reactance compensation voltage, will be lagging the correct, on horizontal, phase angle by 30 degrees, so that if a compensator current of 30 degrees lead flows through the compensator, the resistance compensationvoltage will be brought into the proper phase relation to secure true resistance compensation. i

The rectangle composed of the continuous vectors represents conditions in Fig. 2 and with one exception the operation will be obvious from what has already been said. This exception relates to the reactance compensation voltage. l lormally the voltage drop through a capacitor leads the current by 90 degrees. That would have produced a phase shift of the reactance compensation voltage in Fig. 2 of 150 degrees in the lagging direction instead of the desired 30 in the leading direction. Correction is secured by reversing the direction of the capacitor voltage drop by 'means of the transformer ll.

By adJusting the slide wires on resistors 8 and Ill in Figs. 1' and 2, the magnitude of the resist- .ance and reactance compensation may be adjusted at will.

In Fig. 8, the compensators of Figs. 1- and 2 have been combined into a single compensator which, in "addition, by means of the proper manipulation of four switches l5, i6, i1 and [8 may also be adapted-*ior single phase operation. Thus, if switches: i and I6 are moved to the positions.

labeled 1 5 (single phase) and switches i1 and i8 are left in their mid-positions, the current transformer current will flow through adjustable portions of resistor 8 alone, and after leaving resistor'd will divide, part of it flowing through the left hand portion of resistor Ill and the rest o'f-itdlowing through the reactor ii and the capacitor 13' in series and back .to the current transformerthrough the right hand part of the resistor ll. The reactor H and the capacitor I! usually are equal in magnitude so that this branch of the circuit-is series resonant and produces no phase shift of the compensator current. Consequently, there are. inserted in series 5 with the relay! a resistance compensation voltage corresponding to the voltage drop in resistance l and a reactance compensation voltage corresponding 'to'the voltage drop in reactor ii, and this will give true compensationprovided the potential transformer voltage and the current transformer current are in phase at unity power factor as they'will be in a single phase circuit, and if reactor H has negligible resistance. If now switch I5 is thrown to the position labeled 15 31 i (3phase) and switches l6, l1 and it are moved to their leading or lagging positions, the compensator connections produced thereby will respectively be. the equivalent of Figs. 1 and 2.

Auxiliary resistors l8 and i9: are connected in series with the primary relay by the switch IS in its I i-phase positions in order to "compensate the voltmeter circuit for the change in compensator impedance when going from single phasev to 3-phase operation. The switch ii in going from its single phase to its 3-phase position changes the ratio of the current transformer in order to correct 'for the change in the compensator impedances when going from single phase to 3- phase operation. Thatis to say, in order that the same magnitude of line current will produce the same magnitude of compensation voltage, the

- current transformer ratio must be changed in compensators. However, it differs therefromin do two important respects. The first is that the reversing transformer M for the capacitive reactance of the reactance compensation elements which gives correct compensation with 30.de-

' grees lagging current is eliminated. The second 60 is that taps are eliminated on the current transformer. Switching, which introduces the possibility of open-circuiting the secondary of a current transformer, is always undesirable because of the relatively high voltages involved.

Both of these changes are effected by-the addition of a resistor 20, a tapped reactor 2i and two separate capacitors 22 and 23. The resistor 20 is. arranged to be connected in parallel with the main slide wire resistance 8 of the resistance 60 compensation element during single phase operation of the compensator by means of a switch 25, while various portions of the reactor 2i are connected respectively in series with the capacitors 22 and 23 during single phase and 3-phase op- (iii the vector equations below. Fig. 10 represents a generalized element of the compensator of Fig. 9.

l The symbols which are used and which designatet the various'elements in Fig. are defined as follows rs=total resistance of slide wire ter-rheostat.

ri= portion of T5 in parallel with ra, Z1 and Z6.

ra=portion of T5 in series with Z: and Z6.

Zz=a general impedance, containing resistance and inductance or capacitance.

Zs=8. general impedance.

ic= compensation current, proportional to the load current of the regulator. (The very small component of ie which flows through the contact-making voltmeter and potential transformer is neglected. Thus, in is confined to the compensator impedances.)

ec=line drop compensation voltage added to E0.

ex=reactance compensation voltage.

z'v= contact-making voltmeter current.

Eel-voltage supplied by potential transformer, proportional to regulated line voltage at .the regulator.

i1=component of 10 through r1.

iz= component .of ie through Z2.

The object is to determine 8c, the compensation voltage introduced into the contact-making voltmeter circuit by the compensation current, ie. The impedance drops due to is are superposed upon those due to iv, but for purposes oi. analysis and explanation iv can be considered zero without error where the impedance elements are linear. For zero voltmeter current, iv, Equations 1 and 2 are obviously true:.

Solving these simultaneously for is, there is obtained,

potentiome- 1',r Ln T1+I3+Z2+ZB 5+ 2+ t The compensation voltage is, therefore,

' Z2 c 2 2"' u l Equation 3 is the key to understanding why it is that adjusting the slide wire potentiometer does not affect the phase angle of the compensation voltage. It expresses the well known fact that current ic divides between the two branches of a parallel circuit (branches 1'1 and 1's-I-Z2+Zs) in such a manner that the current in one branch i:

is directly proportional to the impedance oi. the

other branch 11 and inversely proportional to the vector sum of the impedances in both branches (Tl+T3+Z2+Z6). The sum of the impedances in the two branches has the same magnitude and angle for all positions of the slide wire, and the impedance angle of r; is zero for all positions. Therefore, the phase angle between i: and ie is constant. Since the compensation voltage 6c is the impedance drop i2Z2, and since Zz has a fixed magnitude and angle, the phase angle between cc and ic must therefore be constant.

Three significant points should be noted in Equation 4. First, the compensation voltage 6c is directly proportional to the. compensation current ie as it should be. Second, the impedances in the parentheses are all constant and independent of the rheostat setting. ,They determine the phase angle between es and 10, but permit a linear control of the magnitude of e0 as n is varied from zero to its maximum value. The third point is that only Z: appears in the numerator oi the expression, whereas the sum of Z: and Z; appears in the denominator. Thus the impedance angle of the numerator may be of opposite sign from that oi. the denominator permitting either positive or negative compensator impedance angles greater than 90 degrees. In practice, any angle between about l50" and +l50 can be obtained. For the compensator we use 0, +30, +90 and +120.

In Fig. 9, the same symbols used in Fig. 10 have been applied to the corresponding impedance elements and in addition, further symbols which are self-explanatory have been applied to the impedance elements present in Fig. 9 which are not present in Fig. 10.

With the switch handle 28 in the position shown, the resistance compensation element conway, the magnitude of the resistance compensation voltage for any given position of the slide wire will be the same for a given compensator current regardless of which position the switch handle 28 is in. The switch 26 connects the capacitor 22 in series with a tapped portion of the reactor 2l such that the capacitive and inductive reactance elements are equal. Thus, the reactance compensation element of Fig. 9, with the control switch in its single phase position, corresponds exactly to the reactance compensation element of Fig. 8 when it is connected for single phase operation.

If the control handle 28 is now moved to the 30 or 3-phase leading current position, the capacitor 9 is connected in parallel with the resistor 8 in the resistance compensation element and the whole reactor 2| isconnected directly in parallel with the resistor I 0 in the reactance compensation element. This corresponds to the arrangement shown in Fig. 1.

If now the handle is moved to the +30 or 3- phase lagging current position, the resistance compensation element consists of the slide wire resistor 8 which is paralleled by the/reactor l2 and thus, the resistance compensation element j n 1 2 (5) 5+J 2 a) if the resistances of the reactor and capacitor are neglected. Since ex should be 90 ahead of ie with no phase shift, the values of 0:2 and we should I be such that it is 120 ahead of ic with a positive 30 degree shift.

Therefore, make and as. seen from the drawings, 7's=(T1+T3).

Substituting these values in Equation 5 we have Thus, the relative values of the impedance elements in Fig. 9, assuming ideal reactors and capacitors which have no resistance are as follows:

However, for an economical design of compensator which will occupy a reasonably small 35 space, the reactance elements must have appreciable resistance. The presence of this reactance makes necessary a proportioning of the .various impedance values different from those withthe theoretically "pure reactances. While there 40 does not appear to be any simple rule for determining the impedance values for these conditions, nevertheless, it has been found by both out and try calculations and by experiment that precise compensation can be obtained with rela- 5 tively high resistance reactors provided that all resistances and reactances are chosen correctly.

The modification shown in Fig. 11 is fundamentally and theoretically the same as Fig. 9 but it represents a somewhat simplified and more 50 practical arrangement. The most important simplification is that a single capacitor 29 has been substituted for the three capacitors 9, 22

and 23 of Fig. 9. Capacitor 29 has associated.

therewith a tapped auto-transformer 30 which 55 serves a number of purposes. "The first purpose I is to increase the voltage across the capacitor to an economical value and thus reduce the microfarad rating. Another purpose is readily and economically to adapt capacitors whose ratings go vary according to commercial tolerances to the compensator circuit. This is done by means of taps on the high voltage output side of the transformer 30. The remaining purpose of the transformer 30 is readily to permit adjustments as to be made in the effective capacitance value of the capacitor so that the single capacitor 29 may successively have values corresponding to those of capacitors 9, '22 and 23 of Fig. 9. This is done by means of the taps on the low-voltage input 70 side of the auto-transformer.

Another feature of Fig. 11 is the switching arrangement employed. This consists of three 8-pin sockets 3|, 32 and 33, each of which is adaptedto receive the 8-pin plug member 34. 75 These sockets may be standard 8-pin radio tube the contacts in the plug 32 which are indicated as bridged by the short, heavy bars. will be interconnected. The connections produced thereby will correspond to those produced in Fig. 9 when the handle 23 is in the position illustrated. Thus, the resistor will be connected in parallel with the resistor 8 through the left hand contacts of the socket 32. A portion of the reactor 2| will be connected in series with a portion of the 18 primary of the auto-transformer through the right hand contacts of the socket 32. The topmost contacts will connect the serially related reactor and the transformer in parallel with the resistor Hi. The lowermost contacts will con- *9 nect the relay 5 to the junction of the reactor 2i and the capacitor transformer 30, thus, producing the reactance compensation connection corresponding to that produced in Fig. 9 with the handle 28' in the illustrated position.

Placing the plug 34' in the socket 3| or the socket 33 will produce connections equivalent respectively to those produced in Fig. 9 when the handle 28 is moved to the +30 and 30 7 positions.

There is, however, one exception to the above statement and that is that slightly different values of the reactor 2| are used for the 30 leading and 30 lagging connections, respectively.

This is in order to compensate for the resistance of the reactance 2|, as well as for the resistance 1 of the various other reactance. of the circuit.

By way of example, but not by way 01' limitation, the following numerical values are given for a practical design of compensator of the 40 type illustrated in Fig. 11. The compensator is designed to give a maximum of 24 volts, each of resistance and reactance compensation in 'a voltmeter circuit having a nominal current oi. 0.05 ampere. ing table correspond to those used in Figs. 9 and 10. The two values of X2 are obtained by different tap connections between the reactor 2| and the left hand contacts of the sockets 3| and 33. Impedance values are effective, including for 60 example, in the case of the capacitor, the effects of the auto-transformer. Resistances of reactors and capacitors have the same subscripts as to the corresponding reactances.

The use of a slide wire resistor or potentiometer type rheostat for adjustingthe voltage is 76 The subscripts used in the follow- I not an essential part of the invention. Thus in Fig. 12 an adjustable ratio transformer 35 is interposed between the current transformer and the phase shifting circuit, while in Fig. 13 an adjustable reactance transformer 36 is substituted for the simple reactor X.

The modification shown in Fig. 14 differs from Fig. 9 principally in that the reactance compensation element contains an adjustable reactance transformer 36, as shown in Fig. 13, instead of a slide wire resistor. This requires a slight rearrangement of the parallel phase shifting impedances in the reactance compensation element. The arrangement is such that for single phase operation the switch 26 merely connects a portion of the secondary winding of the reactance transformer 36 in the circuit of the voltage relay 5 in series with the resistance compensation element. For three-phase operation the switch :0 26 connects a resistor 39 in parallel with a different amount of the secondary winding of the reactance transformer 36 for the 30 degree leading condition of operation and connects a part of the resistance 39 in series with a capacitor 40 across the secondary winding of the reactance transformer 36 for the 30 degree lagging other condition of operation. The resistance compensation element of Fig. 14 is substantially the same as the resistance compensation element 'of Fig. 9.

Instead of using slide wire adjusters, as in Fig. 9, Fig. 14 employs dial type tap switches 31 and 31' for the resistance compensation element and 38 and 38' for the reactance compensation element. Switches3l and 38 provide for relatively coarse adjustment and switches 31 and 38 provide a relatively fine adjustment.

In general, Fig. 15 bears the same relation to' Fig. 14 as Fig. 11 bears to Fig; 9. It shows die-- grammatically the compensator as it is at present contemplated that it will be manufactured. It is provided with five terminals 4|, 42, 43, 44 and 45. Terminals 4i and 42 are the ones to which the voltage measuring device or voltage regulating relay is connected, terminals 4| and terminals of thevoltage measuring device and the reactor is in series in the circuit supplying both the capacitor and the voltage measuring device- These elements are proportioned in accordance with the teachings of the above-mentioned Birchard application with the result that the volt-ampere burden of the voltage measuring circuit on the potential transformer is very much less than when a conventional resistive ballast is employed and with the further result that i the current in the voltage measuring device is substantially independent of reasonable variations in temperature, frequency and impedance of the voltage measuring device. Taps are provided on the reactor 41 and these are connected to the respective sockets 3|, 32 and 33. The purpose of this is to change the value of the react ance 41 so as to compensate for changes in the effective reactance of the line drop compensator when the plug 34 is inserted in the different sockets. In this manner, the total effective series reactance which cooperates with the shunt capacitor 46 will remain constant for the various conditions ofoperation of the compensator and, therefor, the maximum eifect of the capacitive and inductive ballast is secured.

While Figs. 3, 10, 12 and 13 have been referred to as compensator elements, that is to say either resistance compensator elements or reactance compensator elements, they are not limited to such use and any of them maybe used alone as complete line drop compensators. For example, if Figs. 3 and 10 would produce the thirtydegree phase shift required for the resistance compensation voltage of three-phase circuits they would also produce complete impedance drop compensation for a single phase line having such resistance and reactance that its impedance angle was thirty degrees. Similarly, the reactance compensation elements shown in Figs. 12 and 13 would produce complete impedance drop compensation for a single phase circuit whose resistance and reactance has such relative values that the line had an impedance angle of sixty degrees. Furthermore, by varying the relative reactance and resistance values of the parallel branch circuits of these figures any desired phase shift can be secured so that line drop compensation of a line whose impedance has any given phase angle can be obtained. When used in this manner the magnitude adjustment consisting of the slide wire resistors in Figs. 3 and 10 and the tapson the transformers 35 and 36 in Figs. 12 and 13 would adjust the magnitude of the impedance compensation as a unit and it would be impossible to adjust separately the resistance and reactance compensation components of the total impedance compensation, as isdone in 2, a, 9, 11, 14 and 15.

While there have been shown and described particular embodiments of this invention, it will be-obvious to those skilled in the art that changes and modifications can be made therein without departing from the invention and therefore it is aimed in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of the invention.

Figs. 1,

What we claim as new and desire to obtain by Letters Patent of the United States is:

In a line drop compensating system, a compensator element comprising, in combination, a resistor connected in a voltmeter circuit which measures the line to line voltage of a threephase power line, adjustable means for selectively connecting to various points on said resistor a compensator current circuit which carries a current proportional in magnitude and similar in phase to the current in one of the lines .of said power line between which said line to line voltage is measured, and means for shifting the phase of the compensation voltage of said element so as to correct for the unity power factor 30-degree phase displacement between the voltage of saidyoltmeter circuit and, the compensator current comprising reactive means connected in parallel with said resistor.

2. In a line drop compensating system. a compensator element comprising, in combination, a

. reactance connected in a voltmeter circuit which measures the line to line voltage of a 3-phase power line, a serially-connected resistor and an opposite sign reactance connected in parallel circuit relation with said first-mentioned reactance.

adjustable means for selectively connecting to supply circuit to various points on said resistor, the relative'values of said reactive element and resistor being such as to shift the voltage drop various points on said resistor' a compensator current circuit which carries a current proportional in magnitude and similar in phase to the current in one of the lines of said power line be-' tween which said line to line voltageis measured, said reactances being so proportioned with respect to each other and with respect to said resistor as to shift the phase of the voltage across said first mentioned reactance element so as to correct for the unity power factor 30-degree phase displacement between the voltage of said voltmeter circuit and the compensator current.

3. A line drop compensator which is connected in a circuit for measuring the voltage between two conductors of a three-phase power line and which is energized by a current derived wholly from one of said two conductors comprising, in combination, a resistance compensator having a normally fixed reactance element and an adjustable potentiometer type resistor which is set directly in terms of power line resistance, and a reactance compensator having a normally fixed reactance element and an adjustable potentiometer type resistor which is set directly in terms of power line reactance.

4. A line drop compensator which is connected in a circuit for measuring the voltage between two conductors of a three-phase power line and which is energized by a current derived wholly from one of said two conductors comprising, in combination, a resistance compensator having a resistor connected in parallel with a reactance device, a reactance compensator comprising a second resistor connected in parallel circuitrelation with a second reactance device, a potentiometer type adjuster on said first mentioned resistor which is set directly in terms of power line resistance, and a second potentiometer type adjuster on said resistor which is set directly in terms of p'ower line reactance.

5. A line drop compensator for use with single phase and 3-phase power circuits comprising, in combination, a pair of fixed resistors, separate potentiometer type adjusters on each of said resistors which are set directly in terms of power line resistance and reactance respectively, means for shifting the phase of the compensator voltages comprising a plurality of impedance elements adapted selectively to be connected in parallel with said resistors, and 3-positioned switching means for selectively varying the parallel connections between said resistors and said impedance elements so as to provide the correct through said reactance element with respect to a current in said current supply circuit through a predeterminedacute angle.' 1

8. In combination, a relatively high impedance circuit, a reactance element serially connected therein, a branch circuit connected in parallel circuit relation with said reactance element, a

second reactance element of different value and opposite sign and a resistor seriallyconnected ohmic value of l73per centof the ohmic value phase of the compensator voltages for single.

phase and plus and minus SU -degree 3-phase operation.

6. In combination, a relatively high impedancecircuit, an impedance element connected in series circuit relation therewith, a branchcircuit connected in parallel circuit relation with said impedance element, a different kind of impedance element serially connected in said branch cir-,

cult, and means for adjustably connecting an alternating current supply circuit to various,

points on the element in the branch circuit, the

' relative values of said elements being such as-to shift the voltage drop in said first-mentioned element with respect to acurrent in said supply circuit through a predetermined acute angle. 7. In combination, a relatively high impedance circuit, a reactive element. serially connected therein, a resistor connected in parallel circuitof its parallel resistor, an inductive reactance element-connected in parallel with the other resistor which has an ohmic value of 173 per cent of the ohmic value of its parallel-connected reactive element and separate potentiometer type adjustors on each of said resistors adapted to be serially connected in an energizing circuit for said compensator.

10. A line drop compensator comprising, in combination, a pair of serially connected resistors, an inductive reactance element connected in parallel with one of said resistors and having an ohmic value of 173 per cent of the ohmic value of its parallel connected resistor, a capacitor connected in parallel with the other resistor, a reversing transformer for reversing the voltage of saidcapacitor, said capacitor and transformer having an effective capacitive reactance of substantially 58 per cent of the ohmic value of its parallel connected resistor, and separate potentiometer type adjusters on each of said resistors serially connected in an energizing circuit for said compensator.

11. In combination, a potential transformer having a primary winding connected between two conductors of a three-phase power line, a voltage measuring circuit connected to the secondary winding of said potential transformer, a pair of resistors serially connected in said voltage measuring circuit, a reactor, a capacitor, switching means forselectively connecting said reactor or said capacitor in parallel with one of said resistors', a second reactor and a second capacitor, a transformer for reversing the voltage of said second capacitor, said secondreactor and said second capacitor being serially connected with each other in parallel with the other of said pair of resistors, switching means for selectively short circuiting said reactor or said reversing transformer, a pair of slidable contacts on said resistors, a current transformer connected in one of the conductors of the three-phase circuit between which the primary winding of said potential transformer is connected, a circuit containing the secondary winding of said current transformer andsald slidable contacts in series, means for varying the ratio of said current transformer, a voltage sensitive device, a third resistor connected. in series with the first-mentioned pairof resistors, and switching means for selectively connecting said voltage ,sensitive device to said third resistor Q! to a point beand a reactance compensator including a reac-1 tance connected in series with said resistance, and switching means for selectively connecting 1) in parallel circuit relation with a portion of said reactance, serially connected capacitance and a second resistor for single phase operation,

(2) in parallel circuit relation with all of said reactance said second resistance for minus 30- degree 3-phase operation, and (3) in parallel circuit relation with all of said reactance serially connected different value of capacitance and said second resistance for plus 30-degree 3-phase operation.

13. A line drop compensator comprising, in

combination, a first resistor and a second resistor serially connected with each other, a capacitor, a. reactor, a' third resistor, means for selectively connecting said capacitor, said reactoror said third resistor in parallel with the first resistor, a second reactor provided with taps, third and fourth capacitors having values different from each other and difi'erent from the first capacitor, switching means for selectively connecting said second reactor in parallel with said second resistor, connecting said second capacitor in series with a portion of said reactor across said second resistor and connecting said second reactor and said third capacitor in series with each other across said second resistor.

14. In a variable capacitive reactance device, a plurality of pairs of terminals between which it is desired to have difierent predetermined values of eiiective capacitive reactance, a capacitor, a transformer having a low voltage primary winding and a high voltage secondary winding, taps on said primary winding for connection to said terminals and electrically spaced on said winding according to the ratios of effective capacitive reactance desired, and taps on said secondary winding for connecting said capacitor across variable portions thereof so asto correct for manufacturing variations in capacity of said capacitor.

15. In a line drop compensator, a plurality of selectively operable circuits each adapted to contain a capacitor of different value, a single capacitor, switching means for selectively connecting said capacitor in said circuits, and an adapting step-up transformer interposed between said capacitor and said switching means, taps on the secondary side of said transformer for correcting for the effect of manufacturing tolerances, on the value of said capacitor, and taps on the primary side of said transformer for changing the eil'ective value of said capacitor.

16. A line drop compensator adapted for single phase and plus and minus 30-degree 3-phase operation comprising a first resistor and a second resistor each provided withpotentiometer type adjusters, said adjusters being connected re-,

spectively to the out-put terminals of a current transformer, a simple reactor, a reactor provided with taps, a simple resistor, a capacitor provided with a tapped stepup transformer, and switching means for selectively connecting (1) said resistor in series with. said stepup transformer across another portion of said tapped reactor and (3) a diflerent portion of said stepup transformer in parallel with said first slidable contact resistor and said second slidable contact resistor in parallel with a different portion of said tapped reactor.

17. In hombination, a main electric circuit, a pair of branch circuits connected in parallel circuit relation with each other and in series circuit relation with said main circuit, means for circulating anadjustable total current in said branch circuits so as to produce an adjustable voltage drop in said main circuit, and impedance elements of different kinds connected respectively in said branch circuits and being so correlated as to produce a predetermined phase angle relation between said voltage drop and said current.

18. In combination, a line drop compensator having an adjustable resistance compensation element and an adjustable reactance compensation element, said compensator being provided with a pair of output terminals connected in series with a voltametric device across two of the conductors of a polyphase circuit and being further provided with a pair of input terminals energized in accordance with the current in one of said two conductors, and means for causing the voltages of said elements to be in line and in' connected respectively in parallel circuit relation with said elements.

19. In combination, a line drop compensator having an adjustable resistance compensation element and an adjustable reactance compensation element, said compensator being provided with a pair of output terminals connected in series with a voltametric device across two of the conductors of an alternating current power circuit and being further provided with a pair of input terminals energized in accordance with the current in one of the conductors of said power circuit, and means for shifting the phase of the voltages of .said elements so as to secure correct resistance and reactance compensation comprising a pair of impedance devices connected respectively in parallel circuit relation with said elements.

20. In combination, a plurality of impedance elements connected in parallel circuit relation in a relative high impedance circuit for measuring the voltage of a main alternating current circuit which has a resultant impedance consisting of resistance and reactance, and means for causing current derived from the currentin said main circuit to flow in said elements, said elements having such resistive and reactance values as to cause the resultant voltage drop across them to bear the same relation in magnitude and phase to the voltage of said meas-' uring circuit as exists between the resultant impedance voltage drop in'said main circuit and the voltage of said maincircuit.

21. In aline drop compensator for single phase operation, a resistance compensator including a resistance, means for selectively connecting (l) a resistor in parallel with said resistance for single phase operation, (2) a reactor in parallel with said resistance for minus thirty-degree three-phase operation and (3) capacitance in parallel with said resistance for plus thirty-degree three-phase operation, a reactance compensator including a reactance transformer, and switching means for selectively connecting (l) a portion of the secondary winding of said reactance transformer in series with said resistance for single phase operation, (2) connecting a different value of resistance in parallel with a different portion of the secondary winding of said reactance transformer for minus thirty-degree three-phase operationand (3) connecting a third valueof reslstanceand a second value of capacitance in series with each other and in shunt circuit relation with the secondary winding of said reactance transformer for plus thirtydegree three-phase operation.

22. A line drop compensator for use with single phase and three-phase power circuits comprising, in combination, a reactance element and a resistance element, each 01' said elements comprising an adjustable impedance and a plurality of additional impedances for selective connection in parallel therewith, and switching means for making and breaking the parallel connections of said elements comprising three multi-pin receiving sockets, and a common multl-pin plug for cooperating selectively with each of said sockets.

23. In a voltage measuring circuit, a ballast impedance and a line drop compensator connected in said circuit, said ballast impedance requiring substantially constant reactance in said circuit for best operation, switching means for shifting the phase of the voltage of said compensator, said switching means acting to vary the efiective reactance of said compensator, and means controlled by said. switching means for varying the reactance of said ballast impedance in such a manner as to maintain the combined reactance of said ballast impedance and said line 'drop compensator substantially independent of changes in the phase angle of the voltage of said compensator produced bysaid switching means.

WILLARD J. MCLACHLAN. WAYNE E. BIRCHARD. 

